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JPH05236597

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DESCRIPTION JPH05236597
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
ultrasonic probe used as a sensor of a sonar or ultrasonic diagnostic apparatus.
[0002]
2. Description of the Related Art Recently, ultrasonic waves are focused on a portion on the
subject side of an ultrasonic probe which is a sensor such as water or a living body sonar or
ultrasonic diagnostic apparatus to improve resolution. It is common to provide an acoustic lens.
[0003]
Heretofore, this type of ultrasonic probe is known to have the configuration described on page
404 of APRIL VOL. 72 No. 4 1989, the journal of the Institute of Electronics, Information and
Communication Engineers.
Hereinafter, a conventional ultrasonic probe will be described.
[0004]
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FIG. 4 is a partially cutaway perspective view showing an outline of a conventional ultrasonic
probe, in which a plurality of piezoelectric elements 1 arranged in a plurality on a packing
material 2 are provided on the piezoelectric element 1 and the first and second The acoustic
matching layers 3 and 4 are provided. Furthermore, an acoustic lens 5 made of silicone rubber is
provided thereon.
[0005]
The acoustic lens 5 has a function of focusing ultrasonic waves at an arbitrary distance in a
direction perpendicular to the direction of the piezoelectric elements 1 arranged in a plurality,
and generally the contact with the object (not shown) When considered, it is convexly formed of
a material of silicone rubber that is slower than the sound velocity of the subject. Up to this point,
most of them have a convex shape as shown in the figure, because the contact property is
deteriorated when this becomes concave.
[0006]
As described above, since the conventional ultrasonic probe focuses the ultrasonic waves by the
acoustic lens 5, the resolution is improved.
[0007]
However, such a conventional ultrasonic probe is made of silicone rubber although it has the
focusing effect of the acoustic lens when used in a high frequency region of 5 MHz or more.
Since the acoustic lens has a large sound wave attenuation coefficient, high frequency
components are attenuated by the acoustic lens and the frequency characteristic is significantly
reduced.
Therefore, the resolution is degraded due to the attenuation of the silicone rubber acoustic lens,
and the depth of examination is also reduced.
[0008]
The present invention solves such conventional problems, and provides a low attenuation
propagation medium (or acoustic lens) having a curved surface on at least one or more first
acoustic matching layers provided on a piezoelectric body. By providing an acoustic lens (or
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propagation medium) with low attenuation on which the at least one or more second acoustic
matching layers are further provided, thereby reducing the resolution by the acoustic lens. An
object of the present invention is to provide an ultrasound probe that does not cause a decrease
in examination depth.
[0009]
According to the present invention, there is provided at least one first acoustic matching layer
provided on one side of a piezoelectric body, and a curved surface provided on the first acoustic
matching layer. A propagation medium (or acoustic lens) with low attenuation of high frequency
components, an acoustic lens (or propagation medium) with low attenuation of high frequency
components provided along a curved surface of the propagation medium (or acoustic lens), and
the acoustic lens (or And at least one second acoustic matching layer provided on the front
surface of the propagation medium).
[0010]
According to the present invention, since the propagation medium and the acoustic lens having
the material having the small frequency-dependent attenuation characteristics and the small
attenuation coefficient are used, the acoustic lens can be used even with a high frequency
ultrasonic probe. Since the attenuation can be reduced and a wide frequency band characteristic
can be obtained, an ultrasonic image with high resolution and a deep examination depth can be
obtained.
[0011]
Preferred embodiments of the present invention will be described below with reference to the
drawings.
[0012]
(Embodiment 1) FIG. 1 is a cross-sectional view of an essential part of an ultrasonic probe
according to a first embodiment of the present invention.
[0013]
In FIG. 1, 11 is a piezoelectric body for transmitting and receiving sound waves, 12 is a packing
material provided on the side opposite to the side in contact with the subject 18, and 13 is a first
sound provided on the subject side opposite to the packing material 12. Matching layer, 14 is a
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propagation medium having a curved surface 14A provided on the first acoustic matching layer
13, 15 is an acoustic lens having a curved surface 15A provided along the curved surface 14A of
the propagation medium 14, 16, 17 are It is a second acoustic matching layer provided on the
acoustic lens 15.
The surface of the acoustic matching layer 17 is in contact with the object 18.
[0014]
The respective constituent members will be described below.
[0015]
It is desirable that the acoustic impedances Z2 and Z3 of the propagation medium 14 and the
acoustic lens 15 have a value between the acoustic impedance Zp of the piezoelectric body 11
and the acoustic impedance Zb of the subject 18.
[0016]
Further, the sound velocity v2 of the propagation medium 14 and the sound velocity v3 of the
acoustic lens 15 have a relationship of v2 <v3, and the sound velocity v3 of the acoustic lens 15
and the sound velocity vb of the object 18 (vb is 1535 m / s in the living body) Is preferably in
the relationship of v3 <vb.
That is, by setting the speed of sound in the above relationship, the ultrasonic wave can be
focused on an arbitrary distance of the object 18 by the curvature shape of the acoustic lens.
[0017]
Further, the sound velocity v2 of the propagation medium 14 and the sound velocity vb of the
subject 18 are not particularly limited, but the relationship of v2 ≦ vb is better if possible.
However, v2 ≦ vb is not necessarily satisfied because v2 ≦ vb (1535 m / s) and there are not
many materials whose acoustic impedance Z2 of the propagation medium 14 is larger than the
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acoustic impedance Zb of the object 18 and whose attenuation coefficient is small. It is good too.
[0018]
Here, the setting of the acoustic impedance of the propagation medium 14 and the acoustic lens
15 is naturally limited because there are limitations on the speed of sound and the limitations on
the attenuation as described above.
When various materials were searched within these limits, it was excluded because the frequency
dependent attenuation was large or the speed of sound did not match, such as rubber materials,
when the acoustic impedance was about 2.5 MRayl or less.
Therefore, the target acoustic impedance value is the material of the propagation medium 14 and
the acoustic lens 15 having a value between 2.5 MRayl and the acoustic impedance of the
piezoelectric body 11.
For example, the acoustic impedances Z2 and Z3 of the propagation medium 14 and the acoustic
lens 15 are set to a value of about 7 MRayl, and the material of the PZT-based piezoelectric
ceramic is used as the piezoelectric body 11 in an array shape. In this case, the acoustic
impedance Zp of the piezoelectric body 11 is about 28 MRayl, and the Zb of the subject 18 is
1.54 MRayl.
[0019]
Therefore, as shown in FIG. 1, the acoustic impedance Z1 of the first acoustic matching layer 13
provided between the voltage body 11 and the propagation medium 14 is given by the equation
shown in Equation 1.
[0021]
Z1 is approximately 14 MRayl calculated from the equation (1).
That is, Z1 has a value between the piezoelectric body and each acoustic impedance Zp, Z2 of the
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propagation medium.
[0022]
In addition, two second acoustic matching layers 16 and 17 are provided between the acoustic
lens 15 and the subject 18 here, and the acoustic impedances Z4 and Z5 of the respective
acoustic matching layers 16 and 17 are several in number. It is given from the equation shown in
Equation 2 and Equation 3.
[0025] From the equation (2) and the equation (3), the acoustic impedance Z4 of the second
acoustic matching layer 16 on the side of the acoustic lens 15 is about 4.8 MRayl, and the
acoustic impedance of the second acoustic matching layer 17 on the side of the object 18 Z5 has
a value of 2.3 MRayl.
[0026] Needless to say, it is desirable that the sound attenuating coefficients of the propagation
medium 14 and the acoustic lens 15 be as small as possible.
[0027] After the desirable characteristics of the respective constituent materials are clarified as
described above, specific materials of the components excluding the materials of the piezoelectric
body 11 and the packing material 12 will be described below.
[0028] The acoustic impedance Z1 of the first acoustic matching layer 13 is about 14 MRayl, so
if, for example, 1.5 tungsten powder is filled at a volume ratio to vinyl chloride 1, the acoustic
impedance 14.6 MRayl is obtained.
[0029]
In addition to this, it is preferable to use photobale ceramics Z = 14.5 MRayl of Hotton Ceramics
Co., Ltd. or a glass-based material.
In this case, it is desirable that the thickness of the acoustic matching layer 13 be in the vicinity
of a quarter wavelength.
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[0030] Also, as the propagation medium 14, three conditions of acoustic impedance Z2 of about
7 MRayl and sound v2 of 2000 m / s or less (acoustic lens v3 of 2000 m / s or more) and a small
sound attenuation coefficient are satisfied. As the material, used is a material in which powder of
small particle size tungsten powder, tungsten carbide or tungsten oxide is mixed with epoxy
resin. For example, FIG. 2 is a material obtained by filling tungsten powder (average particle
diameter: 0.44 μm) in a weight ratio of 2.0 (A) and 4.0 (B) to epoxy resin ME106 / HY-3081 of
Japan Pelnox and curing it. Acoustic wave attenuation coefficient α (dB / mm) with respect to
the frequency f (MHz) of Further, FIG. 2 shows, for reference, a damping coefficient D of a
general silicone rubber which has been conventionally used.
[0031] As apparent from FIG. 2, the frequency dependence of the conventionally used silicone
rubber is about 0.94 dB / mm / MHz, while the material in which the epoxy resin is filled with
tungsten powder has a value of about 0.43 dB / mm / MHz. , The conventional characteristics of
about one-half. For example, at a frequency of 5 MHz, silicone rubber is about 2.2 dB / mm for a
value of about 4.1 dB / mm. Furthermore, the difference becomes more remarkable as the
frequency becomes higher.
[0032] The acoustic impedance Z2 of the materials A and B in FIG. 2 is 6.1 MRayl and 8.6 MRayl,
and the speed of sound v2 has values of 1970 m / s and 1850 m / s. It has become.
[0033] The acoustic lens 15 has substantially the same acoustic impedance as the propagation
medium 14 and is faster than the sound velocity of the propagation medium 14 and the subject
18, and has a smaller acoustic attenuation coefficient, such as epoxy resin and carbide such as
silicon carbide. A powder, a nitride powder such as aluminum nitride, or a material mixed with a
powder such as alumina is used. For example, the acoustic impedance Z3 of a material obtained
by filling silicon carbide (average particle diameter 20 μm) at a weight ratio of 1.75 into epoxy
resin ME106 / HY-3081 of Japan Pelnox Co. and curing it is about 6.9 MRayl and the speed of
sound is about 3510 m The value is / s.
[0034] Further, the relationship between the frequency f and the sound wave attenuation
coefficient α has the characteristic shown in C of FIG. 2 and this material also has substantially
the same frequency dependence as the material of the propagation medium 14 (A and B of FIG.
2) It has characteristics, and the absolute value of the sound attenuation coefficient has a smaller
value than that of the conventional silicone rubber and the propagation medium 14.
Furthermore, this makes it possible to reduce the sound attenuation coefficient by reducing the
sound attenuation coefficient by decreasing the average particle diameter of the silicon carbide
charged.
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[0035] It is desirable that the speed of sound of the acoustic lens 15 be as large as and faster
than the propagation medium 14 and the object 18 as much as possible. That is, since the
curvature radius of the acoustic lens 15 is large by increasing the sound speed difference, the
thickness of the acoustic lens 15 can be reduced. Therefore, when the epoxy resin is used as the
base material, the sound velocity of the epoxy resin itself is around 2500 m / s, and in order to
make it faster than this sound velocity, the velocity of the powder to be filled is fast such as
carbide, nitride or alumina powder. Is desirable.
[0036] The second acoustic matching layers 16 and 17 are materials having acoustic impedances
Z4 and Z5 of about 4.8 MRayl and about 2.3 MRayl, respectively, and the thickness is the same
as that of the first acoustic matching layer 13. In terms of thinking, it is better to use a quarter
wavelength. For example, as a material of acoustic impedance about 4.8 MRayl, Mitsui Toatsu
Co., Ltd.'s epoxy resin struct bond 7445 (acoustic impedance is 4.5 MRayl) or epoxy resin filled
with silicon carbide at a weight ratio of 1: 1 and cured. The material (acoustic impedance about
4.6 MRayl) is used.
[0037] Further, as a material having an acoustic impedance of about 2.3 MRayl of the acoustic
matching layer 17 on the subject 18 side, a plastic material such as ABS, polystyrene,
polypropylene or the like or Ciba Geigy epoxy resin araldite AW 106 (acoustic impedance is
about 2.4 MRayl) is used.
[0038] By using such a configuration and materials, the acoustic matching layer is formed in
multiple layers and the sound attenuating coefficients of the propagation medium 14 and the
acoustic lens 15 are small even in the case of an ultrasonic probe in a high frequency range. And,
since it is possible to select a material having a small frequency dependency, it is possible to
obtain a characteristic having wide frequency band characteristics and not attenuating high
frequency components. Therefore, an ultrasonic image with high resolution and a deep
examination depth can be obtained.
[0039] In the present embodiment, the case where one first acoustic matching layer 13 provided
between the piezoelectric body 11 and the propagation medium 14 is used has been described,
but in addition, two or more acoustic matching layers may be used. The same or more effects can
be obtained.
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[0040] Further, in the present embodiment, the case of two layers of the second acoustic
matching layers 16 and 17 provided between the acoustic lens 15 and the subject 18 has been
described, but in addition to this, the acoustic of one or three or more layers Similar effects can
be obtained by using a matching layer.
[0041] In the present embodiment, the acoustic impedance of the propagation medium 14 and
the acoustic lens 15 is set to a value near 7 MRayl. In addition to this, the value of the acoustic
impedance between the piezoelectric body 11 and the subject 18 is described. The same effect
can be obtained even when using one having.
[0042] Further, in the present embodiment, the case where the thickness is set to some extent
between the portion having the curved surface 15A of the acoustic lens 15 and the surface to
which the second acoustic matching layer 16 on the opposite side is attached has been described.
In addition, if the thickness of the acoustic lens 15 is a thickness in the range that plays the role
of an acoustic lens, similar effects can be obtained without limitation of the thickness.
[0043] (Embodiment 2) FIG. 3 is a cross-sectional view of an essential part of an ultrasonic probe
according to a second embodiment of the present invention.
[0044] In FIG. 3, the constituent parts are the same as in FIG. 1 of the first embodiment, and the
detailed description thereof is omitted, and only the construction will be described.
[0045] In FIG. 3, a packing material 12 is provided on one surface of the piezoelectric body 11,
and a material having an acoustic impedance value between the acoustic impedances of the
piezoelectric body 11 and the acoustic lens 15 is provided on the opposite surface on the object
18 side. And an acoustic lens 15 having a concave shape with respect to the direction of the
subject 18 and made of a material having a higher sound velocity than the subject 18 and the
propagation medium 14. In the concave shape portion 15B of the acoustic lens 15, the
propagation medium 14 having the value of the acoustic impedance substantially the same as
that of the acoustic lens 15 and the value of the velocity of sound slower than that of the acoustic
lens 15 is provided. Furthermore, on the propagation medium 14, a second acoustic matching
layer 16, 17 (here, two layers) made of a material having an acoustic impedance value between
the acoustic impedance of the propagation medium 14 and each acoustic impedance of the
subject 18 is provided. Configuration.
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[0046] About the characteristic of each component, using the thing substantially the same as
Example 1, you may use the thing of the substantially same material and a shape.
[0047] With such a configuration, even in the case of an ultrasonic probe in a high frequency
range, materials having small attenuation of the acoustic lens 15 and the propagation medium
14 and one having small frequency-dependent attenuation can be selected. And, since the
acoustic matching layer is provided in multiple layers, it is possible to obtain wide frequency
characteristics without attenuating high frequency components. Therefore, an ultrasonic image
with high resolution and a deep examination depth can be obtained.
[0048] By using such a configuration and materials, even in the case of an ultrasonic probe in a
high frequency range, the sound attenuation coefficient of the propagation medium 14 and the
acoustic lens 15 is small, and the frequency dependence is small. There is little attenuation of
frequency components. Therefore, an ultrasonic image with high resolution and a deep
examination depth can be obtained.
[0049] In the present embodiment, the case where one first acoustic matching layer 13 provided
between the piezoelectric body 11 and the propagation medium 14 is used has been described,
but in addition, two or more acoustic matching layers may be used. The same or more effects can
be obtained.
[0050] Further, in the present embodiment, the case of two layers of the second acoustic
matching layers 16 and 17 provided between the acoustic lens 15 and the subject 18 has been
described, but in addition to this, the acoustic of one or three or more layers Similar effects can
be obtained by using a matching layer.
[0051] In the present embodiment, the acoustic impedance of the propagation medium 14 and
the acoustic lens 15 is set to a value near 7 MRayl. In addition to this, the value of the acoustic
impedance between the piezoelectric body 11 and the subject 18 is described. The same effect
can be obtained even when using one having.
[0052] Further, in the present embodiment, although the case where the thickness is made to
some extent between the portion having the curved surface of the acoustic lens 15 and the
surface to which the second acoustic matching layer 16 on the opposite side is attached has been
described, If the thickness of the acoustic lens 15 is a thickness in the range that plays the role of
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the acoustic lens, the same effect can be obtained without limitation of the thickness.
[0053] As described above, in the ultrasonic contact according to the present invention, the first
acoustic matching layer provided on one surface of the piezoelectric body, and the attenuation
having a curved surface on the first acoustic matching layer are small. Since a propagation
medium or an acoustic lens with small frequency dependent attenuation is provided, and at least
one or more second acoustic matching layers are further provided thereon, in the case of a high
frequency ultrasound probe. Also, it is possible to obtain frequency characteristics that do not
attenuate high frequency components. Therefore, it is possible to obtain an ultrasound image
with high resolution and deep examination depth.
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